Tendon injuries, particularly sports related injuries, constitute an increasing proportion of patients treated at our hospital, yet research in the cell biology of tendon healing is in its infancy. Of particular importance in tendon healing is the relationship of exercise and its underlying mechanism. The objective of this study is to explore possible mechanisms, responsible for the effects of mechanical simulation on tendon cell biologic (actin polymerization and cell migration) and biochemical responses (second messengers and matrix adaptations). Specific aims are: 1. to subject tendon and sheath cells to defined mechanical deformation regiments where the amplitude, duration, frequency and strain rates are known; 2. to investigate the mechanism by which mechanical activity is translated into a biochemical signal; 3. to understand how collagen metabolism is regulated in cells subjected to defined cyclic stretching in vitro. An instrument has been developed in my laboratory that will be used to apply regulated mechanical strain to collagen coated, flexible bottomed culture plates that support tendon cell adherence and growth. A mathematical expression relating a response of a cell to the mechanical factors, elongation, frequency and strain rate will be used to model experiments in culture that mimic physical activity experienced by tendon and sheath in vivo. Osteoblasts and endothelial cells are stimulated to divide by one regimen of cyclic strain whereas smooth muscle cells and pulp fibroblasts are retarded while tendon cells are refractory. Other responses such as alteration in protein synthesis and collagen metabolism specifically have been noted. An examination of key second messenger signalling pathways, such as, cAMP, PGE2, diacylglycerol and phosphoinositides will be performed using radioimmunoassay, chemical separation and protein kinase C measurements. Mitogenic responses of cells will be assayed by quantitation of DNA synthesis directly in stimulated cells and in conditioned medium. Collagen metabolism will be monitored by quantitation of mRNA, collagen synthesis, type an crosslink quality an quantity. Modelling the impact of physical deformation on tendon cells in culture may yield a quantitative solution to which exercise regimens work best in vivo to yield a healed tendon that is strong yet flexible.